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How Does an Unvented Cylinder Work?

Once upon a time, all water heaters installed in the UK were vented to the outside atmosphere. However, that changed in 1986, when unvented cylinders were made legal. These allowed homeowners to enjoy a number of benefits that were not possible with older, unpressurised types. Today, unvented cylinders are very popular, but how do they work?

Unvented Cylinder Operation

With vented cylinders, the water heater had to be installed in an attic or another location where gravity combined with the pressure of the mains could move heated water down through the pipes to the taps. This limited your ability to install water heaters in some homes, and also meant that hot water pressure at the taps was usually low.

Unvented cylinders, on the other hand, are pressurised, and can supply mains-pressure water anywhere in a home without the need to be installed in an elevated location.

An unvented cylinder is connected directly to the mains water supply. It uses electricity or gas to heat water to a pre-set temperature. The act of heating water causes it to expand, which creates pressure within the cylinder. That pressure pushes the water outward throughout your home’s pipes.

However, because water expands when it is hot, there is a need to account for this additional space needed. An expansion vessel is attached somewhere to the system to handle this need. It may be attached to the cylinder, attached to the hot water system somewhere else, or even be part of the cylinder itself.

Your unvented cylinder also includes additional safeguards against overpressure situations, such as a pressure reducing valve to limit incoming pressure and an expansion relief valve to allow overheated water to be discharged. A temperature and pressure relief valve is also fitted to your cylinder to provide additional protection.

While unvented cylinders are safe for use within UK homes, they must be installed, maintained, and repaired by plumbers certified to work with unvented water heaters. If you’re experiencing any problems with your unvented cylinder, or would like to have annual maintenance performed, EasyFlow can help. We cover the areas of Greater Manchester, Liverpool, Chester and Leeds. Call us on 0161 941 5571